(1) Field of the Invention
The present invention relates to a method of testing squamous epithelial cells. The present invention also relates to a method of screening therapeutic agents for squamous cell carcinoma.
(2) Description of the Related Art
Since the discovery of a basic fibroblast growth factor (FGF-2) as a growth factor for fibroblasts in the early 1970's1), the fibloblast growth factor (FGF) family that is encoded by 21 different genes has been elucidated up to now2). The activity of FGF is mediated by a high-affinity FGF receptor (FGFR) on the cell surface, and FGF has a structure composed of two or three extracellular immunoglobulin-like loop structures (1 g), a transmembrane domain, and, within the cell, a tyrosine kinase region divided into two parts3)-5). It has been believed that FGFR, when bound to FGF in the presence of heparin or heparan sulfate proteoglycan, forms a dimer, which self-phosphorylates the tyrosine residue of the receptor or reciprocally phosphorylates each other, and transduces signals of cell growth, differentiation, and the like6)-8).
As the genes encoding FGFR, four types of genes have been identified17) such as FGFR19)-11), FGFR211),12), FGFR313),14), and FGFR415),16). Furthermore, it is known that, due to differences in selective splicing of exons encoding the immunoglobulin-like region (IgIII) corresponding to the extracellular ligand binding site, there are two types of splicing variants for each of FGFR1, FGFR,2, and FGFR318),19), and a total of seven types of FGFR are known. Each FGFR has different binding ability17),20)-24).
Recently, it was shown that anomalous FGFR causes various congenital skeletal and chondral dysplasia. It is reported that an anomalous FGFR1 gene causes Pfeiffer syndrome, an anomalous FGFR2 causes Crouzon syndrome, Jackson-Weiss syndrome, Pfeiffer syndrome, Apert syndrome and the like, an anomalous FGFR3 causes achondrogenesis and chondral hypoplasia, Crouzon syndrome complicated by acanthosis nigricans, thanatopholic dysplasia (type 1 and 2), FGFR3-related coronal synostosis syndrome, and the like25),26).
For example, mutations or Cys342Tyr, Ser354Cys, Tyr340His, etc. in FGFR2 for Crouzon syndrome36)-38) which is a lusus naturae complicated by coronal synostosis, Pro252Arg in FGFR1 for Pfeiffer syndrome39)-42), Ala344Gly in FGFR2 for Jackson-Weiss syndrome37), and Ser252Trp and Pro253Arg in FGFR2 for Apert syndrome43) are known. Furthermore, mutations of Gly380Arg in the FGFR3 transmembrane domain for achondroplasia44),45), Arg248Cys in FRFR3 for thanatophoric dysplasia type 1 (TDI)46), Lys650Glu in FRFR3 for thanatophoric dysplasia type 2 (TDII)46), Ala391Glu in FRFR3 for Crouzon syndrome complicated by acanthosis nigricans47), and the like have been reported. In the analysis of FGFR molecules in these congenital diseases, permanent tyrosine-phosphorylating activity due to dimerization of receptors per se independent of ligands was observed, and the degree of tyrosine kinase activation of the receptor is thought to be correlated with the severity of the diseases25).
Squamous cell carcinoma is a cancer on the stratified squamous epithelia that mainly cover the skin, the oral cavity, the esophagus, the vagina, the brohchus, and the like, and one of the most frequently seen skin cancers next to basal cell carcinoma. It is reported that any of the above four types exhibits FGFR in the cells of oral squamous cell carcinoma and in normal oral mucosa-derived epithelial cells, but their growth in the normal epithelial cells depends on FGF whereas in the cells of oral squamous cell carcinoma it does not depend on FGF37),38).
In gene diagnosis, the association of gene mutation with a disease is important. However, mutations of the FGFR gene have conventionally been reported on multiple myeloma, bladder cancer, cervical cancer or colon cancer (Nature Genetics, 260-264 (1997); Nature Genetics, 23: 18-20 (1999); and Cancer Research, 60(15): 4049-4052 (2000)), and no such reports have been made on squamous cell carcinoma. Thus, if the association of the FGFR gene with cancer for squamous cell carcinoma, in particular oral squamous cell carcinoma, it would be useful for the development of methods for diagnosing cancer diseases, and the screening and development of therapeutic agents thereof.